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Tuesday, June 8, 2021

SPC Jun 8, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0252 PM CDT Tue Jun 08 2021 Valid 082000Z - 091200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN MONTANA/FAR WESTERN NORTH DAKOTA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE ARKLATEX AND MID-SOUTH... ...SUMMARY... Very large hail, severe wind gusts and a couple tornadoes are expected this afternoon into tonight across the northern High Plains, while severe storms will also be possible across the ArkLaTex region and Mid-South. ...20Z Update... Only change to the previous outlook was to trim behind the ongoing convective line over the Arklatex. As mentioned in the recently issued MCD #885, isolated strong to locally severe gusts will be capable of wind damage as the line segment over northern LA moves to the MS River over the next 1-2 hours. Elsewhere, forecast outlined in the previous discussion (appended below) remain valid. The highest probability of severe thunderstorms remains over northeast MT, where supercells are expected later this evening. All severe hazards are possible with these storms, including very large hail over 2" diameter and wind gusts over 70 mph. ..Mosier.. 06/08/2021 .PREV DISCUSSION... /ISSUED 1154 AM CDT Tue Jun 08 2021/ ...Northern High Plains including Dakotas/eastern Montana... Have upgraded to a categorical Enhanced Risk across eastern Montana and nearby far western North Dakota for an anticipated round of severe storms that will begin by late afternoon and culminate this evening across the region. Influenced by the approaching shortwave trough/speed max over the central Rockies and orographic lift/differential heating, such initial development is expected to begin over/near the mountains of southern Montana, with other development along the north/south-oriented surface trough near the Wyoming and western South Dakota/Nebraska border vicinity. Some initial supercells can be expected, particularly with the development across Montana. Very large hail and a couple of tornadoes could occur particularly late this afternoon through early evening, although upscale growth in a northeastward-racing cluster capable of wind-driven hail/damaging winds seems likely this evening particularly across eastern Montana and possibly far western Dakota. This is generally where deep-layer/low-level winds will be maximized in collocation with a somewhat greater reservoir of moisture/instability near/north of the surface low and front. The severe threat southward near the dryline/lee trough will be more wind-driven, with deep shear weakening southward and convection more high-based. Very well-mixed sub-cloud layers will enable intense downdrafts from any sustained convection that can develop. The threat may last for a few hours before nocturnal boundary-layer cooling more-strongly stabilizes the near-surface layer. ...ArkLaTex/Mid-South... An outflow reinforced effective boundary extends west/southwest to east/northeastward across southern Arkansas into northern Mississippi. While persistent rainfall continues to reinforce the boundary particularly across northern Mississippi, some modification/northward recovery may occur this afternoon in advance of multiple MCVs located across far northeast Texas and southwest Arkansas at midday. As the boundary layer heats and moderately to strongly destabilizes near/south of the aforementioned boundary, some MCV-related enhancement will support semi-organized storm modes, but mostly likely in a quasi-linear fashion although some supercells are possible. Heavy rainfall aside, damaging winds should be the primary risk along with some tornado potential through early evening. ...Upper Ohio Valley/Northeast States... While both deep-layer winds and mid-level lapse rates are weak, a moist/moderately unstable environment this afternoon may yield a few microbursts with strong/locally damaging winds a possibility on a very isolated basis. Read more LIVE: spc.noaa.gov